Swine flu: a timeline

April 24, 2009Health authorities around the world go on alert as the World Health Organisation announces that several hundred cases of swine flu in humans have been signalled over the past weeks in Mexico.They include what is eventually identified as around 15 fatalities, although many more are initially blamed on the virus, while there are nearly a dozen cases in the United States.Mexican authorities speak for the first time of an "epidemic." More than one thousand people in the country are placed under observation.Schools, universities, theatres and museums are closed down in Mexico City and the centre of the country to prevent the spread of the disease.Neighbouring Latin American countries declare health alerts or announce preventative measures.April 25The WHO warns of the "pandemic potential" of the new swine flu virus, which can be transmitted from human to human.More cases are found in the United States.Mexico toughens measures against the disease and orders people who are sick or showing symptoms of the disease to be isolated.April 26The United States declares a health emergency after the confirmation of a total of 20 cases in the country, including eight New York students. (Click more for full timeline)

Here is a timeline of the spread of swine flu, known officially as "influenza A(H1N1)", since it was detected last month:

April 24, 2009

Health authorities around the world go on alert as the World Health Organisation announces that several hundred cases of swine flu in humans have been signalled over the past weeks in Mexico.They include what is eventually identified as around 15 fatalities, although many more are initially blamed on the virus, while there are nearly a dozen cases in the United States.

Mexican authorities speak for the first time of an "epidemic." More than one thousand people in the country are placed under observation.

Schools, universities, theatres and museums are closed down in Mexico City and the centre of the country to prevent the spread of the disease.

The WHO warns of the "pandemic potential" of the new swine flu virus, which can be transmitted from human to human.

More cases are found in the United States.

Mexico toughens measures against the disease and orders people who are sick or showing symptoms of the disease to be isolated

April 26

The United States declares a health emergency after the confirmation of a total of 20 cases in the country, including eight New York students.

Canada announces its first cases of swine flu.

Countries around the world step up vigilance and precautionary measures as the WHO warns that the virus can mutate at any time and become much more dangerous. Public meetings are suspended in Mexico.

April 27

The first confirmed cases in Europe in people who have returned from Mexico, in Spain and Scotland.

The WHO raises its alert level from 3 to 4 on a scale of 6, signalling a "significant increase in risk of a pandemic." It warns that no region in the world is safe from the virus.

April 28

The epidemic continues to progress, affecting all five continents in the world -- from New Zealand through Israel to Costa Rica.

A state of emergency is declared in California.

Several countries suspend their pork imports from infected regions.

April 29

A 23-month old Mexican toddler becomes the first confirmed death in the United States.

The virus spreads in Europe, where first cases are confirmed in Germany and Austria. New cases are declared in Spain, of which one person had not been to Mexico.

The WHO raises to five its level of alert on a scale of six calling on countries to prepare for an "imminent" pandemic.

April 30

The European Union rules out a French idea to suspend flights to Mexico. The WHO does not recommend limiting travel but Britain, Canada, France, Italy and the Netherlands advise people against travelling to Mexico.

Argentina, Cuba and Peru, as well as several travel operators, suspend their flights there.

May 1

Mexico begins a five-day shutdown at the start of a May Day weekend to try to contain a flu epidemic which the government now says appeared to be "not so aggressive" as initially feared.

The first confirmed case of swine flu in Asia is recorded in Hong Kong after a Mexican man who arrived via Shanghai tested positive. Guests and staff at the hotel where he had stayed are placed under quarantine for a week.

The WHO says it has "no doubt" that a successful vaccine against the swine flu virus could be developed within the next six months.

May 2

Mexico says the flu epidemic appears to be "in a stabilization phase", but the toll in the country rises to 19 dead and 454 confirmed infections.

The WHO says 16 countries have officially reported 658 confirmed cases of influenza A(H1N1), but that there is no indication that it has begun to spread in a sustained manner anywhere outside of North America.